1. Field of the Invention
The present invention relates generally to a gas turbine engine, and in particular, to a TBC coating on an air cooled blade or vane in a gas turbine engine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, the blade and vanes in the turbine section are exposed to the highest temperatures in the engine. It is these parts which limit the operating temperature of the gas turbine engine. Higher efficiency is obtained with a higher operating temperature. However, modern materials are limited to operating temperatures below the melting temperature of the material. Air cooling of the blades has been used to allow for higher turbine temperatures without raising the melting temperature of the blades. Thermal Barrier Coatings (or, TBC) have been used on surfaces of the blade exposed to the highest temperatures to further increase the operating temperature of the turbine. TBCs are thin coatings of high temperature resistant ceramic materials that act to block the high temperatures from harming the blade material. TBCs are generally thin of about 1 mm in thickness, and are brittle. Examples of Prior Art TBCs are disclosed in U.S. Pat. No. 6,933,052 issued to Gorman et al, U.S. Pat. No. 6,890,668 issued to Bruce et al, U.S. Pat. No. 6,730,413 issued to Schaeffer et al, U.S. Pat. No. 6,686,060 issued to Bruce et al, U.S. Pat. No. 6,548,190 issued to Spitsberg et al, U.S. Pat. No. 6,485,848 issued to Wang et al, U.S. Pat. No. 6,465,090 issued to Stowell et al, and U.S. Pat. No. 6,444,335 issued to Wang et al, all of which are incorporated herein by reference.
It is desirable to make the TBC layer thicker in order to provide more protection to the airfoil surface from the high temperatures. A thicker TBC layer would allow for higher gas turbine temperatures, leading to improved efficiency of the engine. However, when the TBC layer gets too thick, pieces start to spall or chip off and eventually the underlining airfoil base material is exposed to the high gas stream temperature due to lack of TBC protection. It is therefore desirable to provide for a thicker TBC layer on an airfoil used in the high temperature regions of a gas turbine engine.